IL33916A - Time-delay light-sensitive circuitry for connecting and disconnecting a load - Google Patents

Description

opig **n gin^i man1? niwwn nntao ¾t p TIME-DELAY LIGHT-SENSITIVE CIRCUITRY FOR CONNECTINfl AND DISCONNECTING A LOAD This invention relates to circuitry for connecting a load to, and disconnecting the load from, a current source. Preferably, the load consists of an incandescent lamp or several parallel connected incandescent lamps. The circuitry is specifically, but not exclusively, useful as a so-called automatic staircase time switch which is employed for timed lighting of one or several light sources (incandescent lamps) in public premises that require only temporary lighting while persons are passing through said premises* Al previously known automatic staircase time switches are of the electromechanical type and suffer from the inconvenience and drawbacks associated therewith One of the main drawbacks inherent in prior art automatic stairoase switches is that they can be caused to connect the load thereof to a current source irrespective of whether ambient light conditions make such a connection unnecessary* In other words, the prior art time switches permit lighting of the light sources eve if the prevailing light conditions are fully sufficient* In accordance with the invention there is provided a circuit for connecting and disconnectin a load in the form of several, parallel connected incandescent lamps, comprising! means for eeding a current to said loadf means for switching said load to or from said current feeding means} means for manually actuating said switching means; means for blocking in response to a predetermined ambient light intensity actuation of said switching means by said manual actuation means, and means for automatically disconnecting said load after P.A* a predetermined connecting period; said blocking means including a transistor which when non-conductive is adapted to permit connection of said load via said switching means , and a resistor network, said resistor network including a light sensitive resistor and a potentiometer having a sliding contact connected to the base of said transistor* -la The invention will be more fully described in the following with reference to th accompanying drawings in whicht Figure 1 shows a wiring diagram of circuitry according to the present invention* and Figure 2 shows a wiring diagram of another embodiment of circuitry according to the present invention.

The circuitry illustrated in igure 1 has a pair of input terminals Δ.Β - terminal B also serves as an output terminal or connection for a neutral conductor - and a pair of output terminals C»D. A mains source having a voltage of preferably 220V and a frequency of 50 cycles is connected to the input terminals A»B. A load which in the present instance comprises a number of parallel-connected incandescent lamps L (only one being shown in the drawing) in a staircase lighting system* is connected to the output terminals B>C. A manually operalbe switch circuit which in the present instance comprises a number of parallel-connected push button switches S (again only one of which is shown), is. connected to the output terminals B»D. Built into each of said switches S is a glow lamp G and in series with it a. resistor SR. A capacitor C6 which serves as a suppressor is connected across the input terminals A,B.

The circuitry illustrated in Figure 1 includes a dc supply section which serves to supply a d.c. current to the electronic low current puotion of the circuitry and comprises a resistor Ri» a diode D2, a capacitor Cl» a resistor R2 and a Zener diode 03. The resistor Rl is connected between the input terminal B and the cathode of the diode 02» and the capacitor CI is connected between the anode of the diode D2 and the input terminal A.

The resistor R2 is connected between the anode of the diode 02 and the anode of the Zener diode 03 » the cathode of the Zener diode 03 being connected to the input terminal A.

The high curren circuit for connecting the mains to* and disconnecting the mains from the load» or in the present instance the lamp L, includes a first circuit having a triad 01 and a unijunction transistor T3 for controlling the trlac 01* The triac 01 is connected between the input terminal A and the output terminal C and i s gate is connected to the input terminal A via a resistor R17 and to the emitter of the unijunction transistor T3 via a capacitor C5. The unijunction transistor T3 is connected to the input terminal A via a resistor R16 and to the anode of Zener diode 03· Thus the series combination of the u unijunction transistor T3 and the resistor R16 is connected across the d.c. supply section* The input terminal A is connected to the emitter of the unijunction transistor T3 via a resistor R15 and :a resistor R18. A further unijunction transistor T2 is connected between the connection between the resistors R15 and R18 and the connection between the diode 03 and the resistor R2» while the emitter of unijunction transistor T2 is connected to one terminal of a resistor R9» the other terminal of which is connected to a diode 08 connected In parallel with a resistor R8. The cathode of the diode 08 is connected to the resistor R9 and the anode of - S - the diode D8 is connected to the input terminal A via a variable resistor R13 and to the anode of the Zener diode S3 and the resistor R2 via a series combination of a diode D6 and a capacitor C3. The cathode of the diode D6 is connected to the capacitor C3 and by way of a resistor R7 , to the anode of a thyristor D5. The cathode o the thyristor D5 is connected to the anode of the Zener diode D » while the gate of the thyristor D5 is connected to the anode of the Zener diode D3 via a resistor R6« The gate of the thyristor D5 is further connected) by way of a resisto R5 to the cathode of a diode D4 of which the anode is connected to the anode of the Zener diode D3 by way of a resistor R .

A capacitor C2 is connected between the anode of the Zener diode B3 and the cathode of the diode D » the anode of the latter diode D4 being further connected to the output terminal D via a resistor S3* The described circuitry also includes a blocking circuit comprising a transistor Tl and a resistance network* The collector of the transistor Tl is connected to the input terminal A via a resistor R1 , the emitter of the transisto Tl is connected to the anode of the Zener diode 09 via a capacitor C4, and the base of the transistor Tl is connected to the sliding contact of a potentiometer Rll via a diode D7 of which the cathode is connected to the base of the transistor Tl. The emitter of the transistor Tl is further connected directly to the emitter of the unijunction transistor T2 and the base of the transistor Tl is directly connected to the cathode of the diode DS« In addition to the above mentioned potentiometer Rll* the resistance network includes a resistor RIO and a further resistor £12· The potentiometer Rll and the resistors RIO and R12 are connected in series witherach other, and this series circuit is connected between the input terminal A and the connection between the diode D3 and the resistor R2. The resistor R|2 of this series circuit is a light sensitive resistor* The function of the circuitry outlined in the foregoing will be more fully described in the following* Upon depression of the push button switch S, a triggering the pulse is applied to the gate of thyrlstor D5 via the resistors R3 and R5 , and diode D4. The thyristor D5 conducts, and capacitor C3 discharges through resistor R7 and the thyristor D5. Current then begins to flow through the resistor R13 and the diode D6 whereby the capacitor C3 is again charged* During charging of the capacitor C3, the transistor Tl and the unijunction transistor T2 will be non-conductive and a current will flow through the resistors SIS and R18, which will cause oscillation of the unijunction transistor T3.

When unijunction transistor T3 is conductive* and unijunction transistor T2 is non-conductive, capacitor C5 is charged through a charging path comprising input terminal A, resistor R17, capacitor C5, transistor T3 and the connection between diode D3 andrresistor R2. Additionally* a leakage path for the capacitor C5 will be provided by resistors R18 and R15. When the oscillating transistor 13 is non-conductive, the capacitor C5 discharges through resistors R18 and R1S and a large current passes through resistor R17 producing a high potential across the resistor B¾7 which triggers the triad ID1. Thus* the oscillation of unijunction transistor T3 triggers triac 01 which connects the load to the current source when it is conductive.

When the capacitor C3 has bean charged to a certain level» unijunction transistor T2 is rendered conductive* whereupon the current lowing through the resistor R13 will pass through the resistors 8 and R9 and the diode D8« Thus transistor Tl also becomes conductive, whereby a new current path to the emitter of the unijunction transistor T2 is opened via the resistor R14 and the transistor Tl. Because both the transistor Tl and the unijunction transistor T2 are conductive the potential at the connection between resistors R15 and R18 is substantially equal to the potential of terminal B» and therefore no current flows through resistor R18. Hence transistor T3 stops oscillating and feeding pulses to triac Dl. Thus* the load is disconnected or the lamps L are switched off. Additionally* charging of the capacitor C5 is prevented* The resistor R13 and the capacitor C3 determine the period of time for which the triac Dl conducts and for which the load remains connected to the current source* To make lighting of the system or the lamps unnecessary when this is not required for lighting technical reasons* use is made of the light sensitive resistor R12 which senses the prevailing light intensity and in response thereto blocks or makes it impossible for the transistor T3 to oscillate at high light intensities* The transistor Ti remains conductive as long as it Is not necessary to light the lamps L. The light value at which it is possible to switch on the lamps L is set by means of the potentiometer Rll. The resistor R13 being variable } the period for which the light remains on can also be adjusted* another embodiment of the present invention is Illustrated in Figure 2* This embodiment agrees in principle both in design and function with that illustrated in Figure 1· Identical components in the two figures have been allocated the same reference numerals. It should be observed} however} that the component values may differ slightly* In the embodiment shown in Figure 2 the diode 04 has been dispensed with and the resistor R4 in Figure 1 has been replaced by a capacitor G7 feeding alternating voltage to a glow lamp G when the push button is not depressed* Moreover} the diode D6 in Figure 1 has been replaced by a transistor T4 which delivers a constant charging current to the capacitor C3 as long as transistors Tl and PI and conductive* thereby acting to make the charging of the capacitor G3 as linear as possible so that said capacitor C3 can be smaller and a smaller leakage current is obtained in it, which involves a saving of cost* Further > a resistor R26 is connected between the variable resistor R13 and the input terminal A* Certain changes have also been made in the blocking circuit* The light sensitive resistor R12 has been connected in parallel with a resistor R27 for better matching of the light sensitive resistor R12 to the circuit* In addition* the resistors Rll and RIO have changed places* Still another change in the blocking circuit is that the collector of the transistor Tl is coupled to the base of the transistor T4 and to the anode of the diode D2 via a resistor R25.

The most significant difference between the two embodiments shown in Figs* 1 and 2 resides in the circuit acting to connect the load to the current source* The only components similar to those of Fig* 1 are the resistors RS and R18* The connection betwee the resistor RIS and the resistor R18 is connected to the gate of a unijunction transistor PI of a type that can be programmed and the collector of which is connected to th emitter of the transistor Tl* The emitter of transistor PI is connected to the anode of diode D2. The circuit for connecting the load to the source further includes two cam leme arily connected transistors T5 and T6, the collecto of transistor T5 and the emitter of transistor T6 being connected to one terminal of resistor RIS, which is also connected to the base of a further transistor T7* The other terminal of resistor R18 is connected to resistor R15* The base of transistor T5 is connected to the emitter of the unijunction transistor PI via a resistor R19» while the emitters of transistors T5 and T7 and the collector of transistor T6 are connected directly to the emitter of the programmable unijunction transistor PI. Futhermore, the base of the transistor TS and the base of the transistor T6 are each connected to the output terminal B via resistors R2d and R22 respectively* The base o the transistor T6 is connected to the collector of the transistor TS via a resistor R21. The collector of the transistor T7 is connected to the gate of the triac Dl via a resistor R23* As already mentioned, the function of the circuitry illustrated in Figure 2 agrees in principle with that of the circuitry of Figure 1· For elucidatory purposes* the function of the circuitry illustrated in Figure 2 will, however, be described in detail hereinafter. The capacitor C2 serves as an interference filter and prevents ignition of the thyristor D5 by means of transients via the resistors R3 and R5. A pulse from push button S travels via the resistors R3 and R5 to the gate of the thyristor D5 thereby triggering the thyristor D5 which conducts discharging capacitor C3 via resistor R7* Upon discharge of capacitor C3, transistor T4 is rendered conductive, and current flows through resistors R26 and R13, transistor T4, resistor R7 and thyristor D5* While current flows along this path, transistor T and unijunction transistor P are both non-conductive* Thus, transistor T5 becomes non-conductive, and current will flow through resistors R1S and R18 and render transis or T7 conductive* As transistor T7 conducts it triggers trlac Dl which also conducts, thereby connecting the load, lamp L, to the current source* The current flowing through resistors R26 and R13 and transistor T4 recharges the capacitor 03 > and when capacitor C3 is recharged, unijunction transistor PI becomes conductive. As a result the current flowing through resistors R8 And R9 causes a voltage drop across the resistor R9 which renders transistor Tl conductive* Current will therefore low through the resistor R14 and the transistor Tl to the collector of the unijunction transistor Pi. When unijunction transistor PL conducts the resistance across it is low* of the order of 1 ohm, and therefore the potential at the junction of resistors R15 and R18 is substantially equal Co the potential at B. Accordingly* the potential at the base of transistor T7 is too low to allow conduction thereof* and the transistor T7 is rendered non-conductive. Therefore* pulses are not fed to the triac Dl* and the load is therefore disconnected from the current source* The light sensitive resisto R12 produces a certain current when it is exposed to light of a given predeermined intensity* This current flows through part of the resistor Rll and the diode D7 and will render transistor Tl conductive. Thus* even if the push button S is depressed* and thyristor DS conducts as a result* and capacitor C3 is conductive because transistor Tl is conductive* The voltage at the junction of resistors R15 and R18 will be low* and therefore transistor T7 will be non-conductive* While transistor T7 is non£conductive* triac 01 cannot conduct and the load remains disconnected from the current source* After release of push button S, capacitor C3 will again be charged, and the charging current will retain transistor Tl and unijunction transistor PI conductive so that the load remains disconnected from the current source* If; the light intensity falls below the give predetermined value* transistor Tl will be rendered non-conductive when capacitor C3 is discharged, whereby transistor PI also ceases to be conductive and the load is then connected to the current source.

Whenever the potential at terminal B equals the potential at terminal A neither transistor T5 or transistor T6 is conductiveI and transistor T7 is rendered conductive fay the current flowing through resistors R15 and R18 (if transistors T and Pi are* non-conductive). If the potential at B is higher than that at A, transistor T5 will conduct, because of the potential applied to the base of transistor T5 via resistor R20» and transistor T5 will provide a current path for the current in resistors R15 and R18. Transistor T7 is thereby rendered non-conductive* Similarly, when the potential at B is loner than that at A, transistor T6 will conducts because of the potential applied to the base of transistor T6 via resistor 822, and transistor T6 thereby provides a current path for the current in resistors R15 and R18. Transistor T7 is thereby rendered non- conductive* Hence , transistor T7 is only conductive when the potential at A equals the potential at B, that is when the alternating voltage applied between A and B equals zero. It therefore provides pulses for triac Di.

Claims (5)

P.A. 33916/3 WHAT IS CLAIMED IS:

1. A circuit for connecting and disconeecting a ..load in the form of several parallel-connected incandescent lamps« comprising: means for feeding a current to said load; means for switching said load to or from said current feeding means;^means switching means; means for blocking in response, t.o„ajpre- determined ambient light,intensity actuatnon f^JLd__^ ^switching means by said manual actuation means; and means for automatically disconnecting said load after a predetermined connecting period; said blocking means including a transistor which when- non-conductive is adppted to permit connection of said load via said switching means, and a resistor network, said resistor network including a light- sensitive resistor and a potentiometer having a sliding contact connected to the base of said transistor. -.,... ·,· - - - ■■- - ·- - . ...

2. A circuit according to Claim It, wherein said switching means includes a first unijunction transistor operating as an oscillator, a triac the gate of whic is connected to the gate of the unijunction transistor via a capacitor, and a second unijunction transistor whl&h when caused to become non-conductive is adapted to cause the triac to connect said load.

3. A circuit according to Claim 2, wherein said meane for automatically disconnecting said load after a predetermined connecting period includes a capacitor adapted, during charging, to keep said transistor and second unijunction transistor non-conductive, whereby the triac will maintain the load connected during charging of the capacitor. P.A. 33916/3

4. A circuit according to Claim 1, wherein said switching means includes a triac, a unijunction transistor of a type that can be programmed, a complementary transistor pair and a further transistor pair the collector of the unijunction transistor being connected to said blocking means, the gate of the unijunction transistor being connected to the emitters of said complementsry transistors and the base of said further transistor via a resistor, and the collector of said further transistor being connected to the gate of said triac.

5. A circuit for connecting and disconnecting a load substantially as described with reference to and as illustrated in the accompanying drawings. COHEN ZEDEK & SPISBACH P.0. Box 33116 , Te l - A v i * Attorneys for Applicant